Overnight a ~7GB update was D/L-Installing, which was removing my L4D2(part of) and replacing it w/ another game I owned in the past but didn't have installed. After the flush everything is titled correctly but now L4D2(part of) is having to re-download and install which is showing ~7 GB

Completely exit the Steam client.Open the run dialogue by pressing windows key + r (you can also navigate here from the start menu by typing run).Type steam://flushconfig then press enter. (If asked to allow this website to open a program, please click Allow or OK).Restart your computer.Now, launch Steam directly from the installation folder, not from a pre-existing shortcut (~C:\program files (x86)\Steam). The Steam application will either appear as Steam or Steam.exe depending on whether your settings show file extensions.